Absorbent products

ABSTRACT

An absorbent product, for example a diaper, comprises an absorbent member (3), for example a pad formed of comminuted cellulose fibres or a superabsorbent polymer, and a particle-bonded nonwoven material (1) having an outer phase (4) that is in an unlofted state and an inner phase (5) that is in a lofted state. The nonwoven may be formed of polyester fibres bonded with a polyester adhesive. The product may also comprise a liquid-impermeable backing sheet (2).

FIELD OF THE INVENTION

The present invention relates to absorbent products, especially suchproducts that are used for the purposes of personal hygiene to collectliquids such as urine and blood exuded from the human body. Suchproducts include those which may be broadly described as "diapers", forexample babies' napkins, incontinence pads for adult use and ladies'sanitary towels.

BACKGROUND OF THE INVENTION

Conventionally, absorbent products for personal use comprise a core ofabsorbent material which is provided with a liquid-impermeable backingintended to prevent loss of the absorbed liquid and thereby preventcontamination of clothing, bed sheets and the like. The surface of theabsorbent product that in use is in contact with the wearer is formed of"coverstock", this being a liquid-permeable sheet material having arelatively smooth surface in order to minimise discomfort to the wearer.Suitable coverstock materials include thermobonded nonwovens, althoughspunbonded nonwovens and perforated films have also been proposed forthis purpose.

It is also known to interpose between the coverstock and the absorbentcore a discrete layer of hydrophobic material which draws liquid towardsthe absorbent core, thereby keeping the coverstock relatively dry and soimproving comfort and reducing the likelihood of skin rashes. Ahydrophobic layer of this type may be referred to as a "dry bridge",since it reduces the re-wetting of the coverstock with moisture from theabsorbent core.

Although the coverstock does not contribute to the absorptioncharacteristics of these products, its use has so far been consideredessential, in order to achieve consumer acceptance.

SUMMARY OF THE INVENTION

It has now been found that coverstock may be eliminated from absorbentproducts whilst maintaining adequate comfort characteristics for thewearer. In particular, the present invention provides an absorbentproduct comprising an absorbent member at least part of which isoverlaid with a sheet of particle-bonded (e.g. powder-bonded) nonwovenmaterial having a first phase that is in an unlofted state and a secondphase that is in a lofted state, the said second phase being between thesaid first phase and the absorbent member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic cross-section through an absorbent product ofthis invention, showing the component layers therein.

FIG. 2 is a flow-sheet showing various stages in the manufacture of atwo-phase powder-bonded nonwoven suitable for use in this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

An absorbent product of this invention comprises a particle-bondednonwoven having first and second phases, as defined above; the use ofnonwovens having one or more additional phases, although not currentlypreferred, is not precluded. The fibres in each phase may be selected,independently of the other phase(s), from natural fibres (e.g. cottonlinters), regenerated fibres (e.g. viscose rayon) and synthetic polymers(e.g. polyesters, such as poly(ethylene terephthalate), polyamides suchas nylon 6 or nylon 6,6, and polyalkylenes such as polypropylene), aswell as any mixtures of two or more such fibres. However, it ispreferred to use polyester fibres in both the first and the secondphase.

The fibres will have a staple length usually of from 25 to 100 mm,preferably from 35 to 60 mm, and a linear density usually of from 0.5 to20 dtex, preferably from 1.5 to 15 dtex.

The first phase will usually have a basis weight ("grammage") of from 10to 50 g/m², preferably 15 to 25 g/m², whereas the second phase willusually have a basis weight of from 30 to 80 g/m², preferably from 50 to60 g/m².

The absorbent member may be composed of a material that isconventionally used in absorbent products such as diapers. Thus, forexample, the member may be formed as a batt of comminuted cellulosefibres ("cellulose fluff"). However, other materials come intoconsideration, for example hydrophilic polymers, especially theso-called "superabsorbent" polymers, particles of which may bedistributed in or on a suitable substrate or matrix, for instance of asuitable fibrous material, e.g. cellulose fluff or a nonwoven web.Particulate super-absorbent polymers are commercially available (e.g.under the Trade Mark "Aqua Keep" from Norsolor, France), as are varioustypes of equipment for applying them to appropriate carrier materials(e.g. the powder-spray equipment from Nordson Corporation, Ohio, U.S.A.;the apparatus utilising a dosing roller available from Santex AG, Tobel,Switzerland; and the fluidized-bed applicator from Chem. FabrikStockhausen GmbH).

Turning now to FIG. 1, there is illustrated an absorbent articles ofthis invention, namely a diaper, which has been assembled from apowder-bonded nonwoven 1 and a liquid-impermeable backing sheet 2,between which is sandwiched an absorbent member in the form of a layer,wad or pad 3. (These components are shown separated in the drawing forreasons of clarity; in practice, however, the nonwoven 1 and theabsorbent pad 3 will be in substantial contact, in order to permit thetransmission of liquid from the former into the latter.) Thepowder-bonded nonwoven 1 comprises a first phase 4, in which the fibresare in an unlofted state, and a second phase 5, in which the fibres arein a lofted ("uncompressed" or "bulked") state and which preferably hasa higher basis weight than the first phase 4. The said first phase 4defines an outer surface 6 of the absorbent product. The surface 6 isthe one that will be situated against the wearer during use and it istherefore desirable that the said first phase 4 should feel soft andsmooth.

The powder-bonded nonwoven material 1 will usually be made ofhydrophobic fibres. Furthermore, it is desirable that the material notonly should be liquid-permeable but also should enable faststrike-through of liquids to occur. These characteristics permit fluidto pass rapidly into the absorbent pad 3 whilst allowing the nonwovenmaterial 1 to remain substantially dry.

The backing sheet 2 may be formed, for example, of an imperviousplastics material; the so-called "breathable" materials can also beused.

The nonwoven 1 and the backing sheet 2 may be held in place relative tothe absorbent member 3 by any appropriate means, for example stitchingor the use of adhesive material. In another embodiment, the nonwovenmaterial 1 is fastened at its perimeter to the backing sheet 2 to forman envelope containing the absorbent member 3. It is also possible tolaminate the absorbent member, if it is of a suitable material andconstruction (e.g. a tissue), to the nonwoven material; this couldrender the structure of the product more stable, improve the efficiencyof liquid transfer into the absorbent material and result in a productof comparatively thin construction.

The absorbent product may have a size and shape appropriate to theintended use. Other components, e.g. fastening tapes (not shown), may beattached, if required. The use of materials placed intermediate theabsorbent member and the nonwoven material is not precluded. Forexample, the absorbent member may be enclosed by tissue paper or thelike. Furthermore, it is possible to employ a nonwoven having, forexample, an extra phase situated between the said first and secondphases and/or an extra phase at the side of the nonwoven adjacent theabsorbent member.

In addition to the elimination of coverstock, the use of the two-(ormulti-) phase, powder-bonded nonwoven offers the possibility of furtheradvantages, e.g. whiteness, low linting, dimensional stability and a lowcontent of extractables (polyester bonding powders, for instance, beingformaldehyde-free).

The nonwoven material to be used in this invention may be produced byforming, preferably by dry-laying, a layer of fibres that willconstitute one of the said first and second phases and depositingthereon, also preferably by dry-laying, a layer of fibres to constitutethe other of the said phases. A particulate bonding material is thenapplied to the resultant layered web and distributed therethrough. Thefibrous web is subsequently passed through a heating zone in which theparticles are softened or melted, and then through a zone in which it iscompressed in order to increase the contact of the molten or softenedbonding material with the fibres after which the resultant material iscooled in order to solidify the bonding material and thereby to bond thefibres at points throughout the fibre matrix.

With this method of manufacture, there will be a measure ofinterpenetration of fibres from the two phases at the junction thereof,this being regarded as an asset in that it helps to preserve theintegrity of the nonwoven sheet material during shipping, conversioninto the end product and use.

The particles of bonding material applied to the fibrous web may be ofany suitable size and shape, for example the rods or granules disclosed,respectively, in U.S. Pat. Nos. 2,880,112 and 2,880,113 to A. H.Drelich. It is preferred to use powdered bonding materials and thisinvention is therefore described hereinafter with reference topowder-bonded nonwovens.

The technology for producing single-phase powder-bonded nonwovens isknown (see, for example, M. F. Meyer, R. L. McConnell and W. A. Haile,"Production of laminates and nonwovens by powder bonding", a paperpresented at the INSIGHT '85 Advanced Forming/Bonding Conference, Oct.27-29, 1985, Toronto, Canada, the teaching of which is incorporatedherein by reference). The production of two-phase (or multi-phase)powder-bonded nonwovens is analogous and the skilled person should beable readily to produce such nonwovens that are suitable for use in thepresent invention. By way of illustration, however, the production of asuitable two-phase nonwoven is described below with reference to theproduction line shown schematically in FIG. 2.

This production line comprises an open-mesh conveyor belt 20 which isdriven around the rollers 22, 24 in the direction indicated by the arrowA. One or more textile cards--represented by the single device 26--areprovided in order to deposit a layer 28 of fibres on the upper flight ofthe conveyor belt 20. Another layer 30 of fibres is deposited on top ofthe layer 28 from one or more further textile cards, represented by thesingle device 32.

One of the layers constitutes the precursor of the first (unlofted)phase of the nonwoven used in the absorbent product of this invention,whereas the other layer of fibres constitutes the precursor of the saidsecond (lofted) phase. These layers can be deposited in either order. Alofting capability may be achieved by the use of fibres that arecrimped; suitable fibres include the crimped polyester fibres, forexample such fibres with hollow cross-sections, that are marketed byEastman Chemical Products Inc. for fibrefill applications.

The two-layer web 34 is passed through a web-spreading section 36 andthen to a zone in which the powdered bonding material is applied to theweb. This zone is represented by the powder-depositing device 38(although in practice a plurality of such devices may be used). Suitablepowderdepositing devices are powder applicators of the known type inwhich a wired roller takes powder into the space between the wires and,upon rotation, drops the powder out of that space onto the fibrous webpassing beneath it. A screw 40 may be provided in order to raise orlower the roller of the powder-depositing device 38. Furthermore, areceptacle 42 is provided in order to catch any excess powder that fallsthrough the open-mesh belt 20, the powder so collected being availablefor recycyling.

It will be appreciated, of course, that as an alternative to mechanicalpowder-depositing devices, other applicators such as a fluidising airspray or an electrostatic spray-gun come into consideration, as dodevices that apply the powder in a liquid carrier or in the form of afoam.

The bonding powder should have a lower melting point than the fibres inthe web; the bonding powder will commonly be of a material having amelting point in the range 80° to 180° C. In general, the bonding powderwill be a thermoplastic material and it should be capable of forming agood adhesive bond with the fibres being used. In a number of cases,especially in the case of polyester fibres, a polyester bonding powderwill be found to be suitable, for example the polyester powdersavailable from Eastman Chemical Products Inc. as hot-melt adhesivesunder the trade mark "Eastobond". Typical polyester adhesives havemelting points of from 110° to 130° C. and are available as coarsepowders (200-420 microns or 70-40 U.S. standard mesh), medium powders(80-200 microns or 200-70 U.S. standard mesh) and fine powders (80microns or less, or finer than 200 U.S. standard mesh), the mediumpowders being preferred when using mechanical applicators. Otheradhesive binders, for example epoxy resins, also come intoconsideration. The amount of powder deposited in the web will usually befrom 5 to 50% of the total fabric weight, preferably from 10 to 20%.

The two-layer web 34, now with bonding powder distributed through it, istransferred from the conveyor belt 20 to a further conveyor belt 44, forexample of Teflon-coated fibreglass, which belt 44 is driven roundrollers 46, 48 in the direction indicated by the arrow B and serves tocarry the fibrous web 34 through an infrared oven 50. Within the oven50, the bonding powder fuses and bonds the fibres of the web at pointswhere the fibres and the bonding material come into contact. Uponleaving the oven 50, the web 34 is subjected to light pressure by meansof the nip roll 52.

It has been found that the strength of the web material can be improvedby reheating. Accordingly, the web 34 leaving the nip roll 52 istransferred to another conveyor belt 54 which is driven round rollers56, 58 in the direction indicated by the arrow C. As it contacts theconveyor belt 54, the web 34 is carried beneath a water-cooledlightweight roller 60. The web is then carried through a second oven 62and thereafter is subjected to further compression by means of the niproll 64. The nip rolls 52 and 64 may be heated during start-up butthereafter cooled during operation. The rollers 46, 48 and 56, 58 mayalso be water-cooled in order to prevent an excessive build-up oftemperature due to the transfer of heat from the oven. The resultant webis then further cooled by passing it around the water-cooled cans 66,68, following which the web is wound into a roll on the winder 70.

The suitable oven temperatures will depend upon the bonding powder thatis used and will be ascertainable from simple trails or from theliterature provided by the supplier of the bonding powder. Typically,however, the oven temperatures will be within the range from 80° to 200°C. The temperature of the web emerging from the ovens 50 and 62 may bemonitored, for example by means of infrared devices 72 and 74,respectively. It will be appreciated, of course, that the infrared ovens50, 62 could be replaced by other heating devices, e.g. calenders,hot-air ovens, steam presses and heated contact cans with non-sticksurfaces. The dwell time of the web in each oven will depend upon theline speed that is achievable (typically from 50 to 100 metres perminute, although higher speeds may be possible) and other factors, butmay typically be from 20 seconds to 2 minutes.

The pressures applied by the nip rolls 52 and 64 will depend upon thematerials used, the desired characteristics of the web and the processline conditions; normally, pressures of up to 30 kg, typically up to 20kg per cm of roll face width are used.

In the powder-bonded, multiphase nonwoven as obtained from thefabric-making line, the thickness of the first phase will be typicallyfrom 0.03 to 0.25 mm. The thickness of the loftable phase will betypically from 0.25 to 1.00 mm but upon lofting to form the second phasethe increase is typically 5 to 10 times, e.g. 7 times, this thickness.

Clearly, a given volume can contain a greater weight of unloftedmaterial than lofted material and it is therefore preferred, for reasonsof economy, to transport and store the sheet material in the unloftedstate prior to its conversion to the end absorbent product. Inprinciple, however, the end absorbent product could be manufactured fromthe nonwoven having a lofted phase as obtained during theabove-described process, after cooling as appropriate.

As indicated above, lofting is, in general, effected by the applicationof heat. Appropriate temperatures and durations of heating may varyaccording to the nonwoven being treated, but will be readilyascertainable by the skilled person. The lofting mechanism may beexplained as follows, with reference to the preferred embodimentsdescribed above. As laid, the precursor of the second phase will bethick and of low density owing to the highly crimped form of the fibresthat are used. When this web is powdered and compressed (e.g.calendered) in the fabric-making process, the adhesive powder bonds holddown the fibres and constrain them in a flat sheet form. It is in this("densified" or "compressed") form that the fabric is removed from thefabric-making line. The lofting process occurs when the adhesive powderbonds are softened by heat. The adhesive bonding material melts at atemperature (typically 110° to 130° C.) that is much lower than themelting temperature of the fibres (typically 250° to 290° C.). Whenheated, therefore, the powder bonds soften and allow the fibres to"regain their memory" and thereby tend to return to the thick, lowdensity form that they were in prior to adhesive bonding. Typically, thelofting temperature will be in the range of 20° to 50° C. above themelting point of the adhesive used. (In general, the fibres of the firstphase will have been chosen so that they do not undergo lofting duringthis heating step, whereby the first phase may retain a surface that iscomfortable to the touch.) The lofted material then cools in its loftedstate and the adhesive resets and thereby stabilises the second phase inits lofted form.

It will be appreciated by the skilled reader that the absorbent articlesof the present invention could be used outside the field of disposablepersonal hygiene aids. For instance, the products may be used in themedical field, as bandaging or as wound dressings (subject to approvalby the appropriate regulatory body).

It will be course be understood that the present invention has beendescribed above purely by way of example, and modifications of detailcan be made within the scope of the invention.

I claim:
 1. An absorbent product comprising an absorbent member at leastpart of which is overlaid with a sheet of particle-bonded nonwovenmaterial having a first phase that is in an unlofted state and a secondphase that is in a lofted state and that has been formed by the heattreatment of a precursor phase comprising crimped fibers, the secondphase being between the first phase and the absorbent member.
 2. Anabsorbent product according to claim 1 in which the absorbent membercomprises comminuted cellulose fibers, a super-absorbent polymer, or amixture thereof.
 3. An absorbent product according to claim 1 in whichthe said first phase has a basis weight of from about 10 to about 50g/m².
 4. An absorbent product according to claim 3 in which the saidsecond phase has a basis weight of from about 30 to about 80 g/m².
 5. Anabsorbent product according to claim 1 in which the nonwoven materialcomprises polyester fibers.
 6. An absorbent product according to claim 1in which the fibres within the nonwoven material are bonded with apolyester.
 7. An absorbent product according to claim 5 in which thefibers within the nonwoven material are bonded with a polyester.
 8. Anabsorbent product according to any one of claims 1 or 2 to 7, inclusive,in the form of a baby's diaper, an adult's incontinence pad or a lady'ssanitary napkin.
 9. An absorbent product according to claim 1 in whichthe nonwoven material is made of hydrophobic fibers.
 10. An absorbentproduct according to claim 1 in which the particle-bonded nonwovenmaterial is a powder-bonded nonwoven material.
 11. An absorbent productaccording to anyone of claims 1, 2 or 9 in which the absorbent member issandwiched between the sheet of particle-bonded nonwoven material and aliquid-impermeable backing sheet.